To get a full understanding of the function and metabolism of vitamin A much further basic knowledge is required. The proposed study aims at elucidating some of the basic characteristics of the retinol metabolism. We will examine the biosynthesis of the vitamin A transporting plasma proteins under various nutritional conditions. These studies should provide information about how the synthesis of the transporting proteins, RBP and PA, is regulated by vitamin A and whether the two proteins undergo post-translational modification prior to secretion. The uptake of vitamin A from RBP will also be explored. Attempts will be made to characterize the cell surface receptor for RBP and antibodies against the receptor will be used to outline its mode of action. The possibility that the receptor for RBP is modulated under various nutritional conditions will be examined. These studies should shed light on the proximate events in the cellular metabolism of vitamin A. We will investigate how vitamin A reaches the cornea under normal conditions and we will examine the quantity and distribution of the new Ia-antigen bearing cells in the normal and in the vitamin A deficient cornea. These studies should provide us with new insight into the metabolism of vitamin A in the cornea and it should be possible to get a better understanding of xerophtalmia and keratomalacia after the completion of these experiments.